It is oftentimes desirable to align optical fibers with an electro-optic device, such as a laser diode. Such alignment is particularly desirable in order to maximize the percentage of light coupled from the light source or electro-optic device to the optical fiber and to thereby increase the transmission efficiency of the optical signals. However, the alignment of optical fibers is complicated by the relatively small sizes of both the optical fiber waveguide, such as a single mode optical fiber which, for example, can have a light transmitting core diameter of approximately 2-10 micrometers, and the light source which has approximately the same size.
The alignment of an optical fiber is further complicated since an optical fiber generally has six degrees of freedom, each of which must be separately aligned. In particular, an optical fiber must generally be aligned in three translational directions, i.e., the X, Y and Z directions, and three rotational directions, i.e., .theta..sub.X, .theta..sub.Y and .theta..sub.Z. Furthermore, the alignment of polarization preserving or polarization maintaining optic fibers is complicated by the need to maintain the polarization axis of the optical fibers in alignment with that of the polarized optical system.
Notwithstanding these difficulties, various methods have been proposed to align a single optical fiber with a variety of electro-optic devices. See, for example, U.S. Pat. Nos. 4,955,683 which was issued Sep. 11, 1992, to Nobuo Shiga, et al. and is assigned to Sumitomo Electric Industries, Ltd.; 4,798,439 which was issued Jan. 17, 1989, to Keith Preston and is assigned to British Telecommunications, PLC; 4,741,796 which was issued May 3, 1988, to Hans Althaus, et al. and is assigned to Siemens Aktiengesellschaft; 4,702,547 which was issued Oct. 27, 1987, to R. Scott Enochs and is assigned to Tektronix, Inc.; U.K. Patent Application GB 2,128,768 which was published May 2, 1984, and is assigned to Hitachi Ltd.; and U.K. Patent Application GB 2,146,841 which was published Apr. 24, 1985, and is assigned to Hitachi Ltd.
As illustrated by these patents and known to those skilled in the art, individual metallized optical fibers can be soldered to a support. In order to position the optical fiber, the solder bonding the metallized optical fiber to the support is generally heated to a temperature above the predetermined melting temperature of the solder. Thereafter, the optical fiber can be moved and, once the optical fiber is properly positioned, the solder can be allowed to cool and resolidify to fix the position of the optical fiber relative to the support and, more importantly, to a light source. These systems typically require, however, some means, such as solder, for retaining an optical fiber in place after the optical fiber has been positioned in a separate alignment process, distinct from the means for retaining the optical fiber in position.
In particular, U.S. Pat. No. 4,798,439 to Keith Preston (hereinafter the "'439 patent") describes an optical assembly and a related method for mounting optical components, such as an optical fiber, on a substrate. According to the '439 patent, an optical fiber is lowered into a layer of solder, such as a solder preform or a solder paste, which has been applied to a submount assembly. Thereafter, a heating element is lowered into contact with the solder to locally melt the solder about the optical fiber such that the optical fiber can be mounted therein. During the mounting process, a first end of the optical fiber is positioned to receive the output of a laser, also illustratively mounted on the submount assembly. By positioning the optical fiber such that the power level of the light transmitted through the optical fiber is maximized, the optical fiber is appropriately aligned with the laser. Once aligned, the heating element is cooled to allow the solder to solidify and to fix the optical fiber to the submount assembly.
Another method of positioning an optical fiber is described in U.S. Pat. No. 4,741,796 to Hans Althaus, et al. (hereinafter the "'796 patent"). In particular, the '796 patent describes a method for aligning an optical fiber with a laser diode. According to this method, an electrically conductive body having a groove defined therein is bonded to a base. An optical fiber extends through the groove and is bonded to the electrically conductive body with a bonding agent. By inducing current flow through the electrically conductive body, the temperature of the electrically conductive body is increased such that the optical fiber is positionable within the bonding agent. After properly positioning the optical fiber relative to the laser diode, the current flow is stopped to cool and solidify the bonding agent, thereby fixing the position of the optical fiber.
While the above-described alignment and bonding systems may controllably position an individual optical fiber, the heat required to allow one optical fiber to be positioned can oftentimes affect the position or alignment of adjacent optical fibers, thereby misaligning the adjacent optical fibers. In addition, these alignment and bonding systems and methods, such as the systems disclosed by the '439 patent and the '796 patent, are generally relatively laborious and time-intensive, particularly, in instances in which a number of optical fibers must be individually aligned.
Accordingly, several commercial alignment systems have been developed to automatically connect, or pigtail, an opto-electronic device, such as a laser diode, to an optical fiber. For example, Melles Griot has developed a system for precisely aligning optical fibers with other optical components. As known to those skilled in the art, however, the Melles Griot alignment system generally includes a variety of relatively complex and costly components which significantly increase the fabrication costs to produce such precisely aligned optical devices. In addition, once the optical fiber has been aligned by a Melles Griot alignment system, the optical fiber must generally be bonded with a separate bonding means, such as solder, as described in the foregoing patents.
One particular application that demands precise alignment of one or more optical fibers involves fiber optic connectors. Fiber optic connectors are commonly employed to align and to interconnect one or more optical fibers with a variety of optical devices or with other optical fibers. For example, fiber optic connectors can be mounted on end portions of a pair of fiber optic cables, each of which include a number of optical fibers. The optical fibers of the fiber optic cables can, for example, transmit data or control signals between various remote devices, such as sensors or actuators, and a central control computer, such as a flight controller of an aircraft. The fiber optic connectors can then be interconnected such that the optical fibers of a first fiber optic cable are aligned with the optical fibers of a second fiber optic cable.
In order to efficiently transmit signals between optical fibers, the fiber optic connectors must precisely align the individual optical fibers such that the optical signals transmitted therethrough are efficiently coupled from fiber to fiber. Such alignment is particularly essential in connecting single mode optical fibers which must be precisely aligned with the light-transmitting core of another single mode optical fiber of similar size in order to efficiently transmit optical signals therethrough.
In order to effectively couple optical signals from fiber to fiber, a fiber optic connector must maintain the precise alignment of the individual optical fibers in a predetermined manner such that the optical fibers will remain aligned as the fiber optic connecter is mated with another fiber optic connector or with other types of optical device. Therefore, a variety of methods as described above have been developed to align individual optical fibers prior to sealing the optical fibers within the fiber optic connector. Since fiber optic connectors typically include a plurality of optical fibers, all of which must be precisely aligned, the alignment process must generally be repeated for each optical fiber of the fiber optic connector prior to hermetically sealing the fiber optic connector. As described above, however, the heat required to allow one optical fiber to be positioned can oftentimes affect the position or alignment of adjacent optical fibers, thereby misaligning the adjacent optical fibers. In addition, these alignment and bonding systems and methods are generally relatively laborious and time-intensive, particularly, in instances in which a number of optical fibers must be individually aligned within the small volume of a single fiber optic connector.
More specifically, a fiber optic connector has been developed by AT&T Bell Laboratories and is described by R. J. Pimpinella in an article entitled "A New Type of Fiber Optic Connector Designed for Military Optical Backplanes", published in the Proceedings of the 42nd ECTC Conference on May 18-20, 1992, pages A-6-1 through A-6-5. This fiber optic connector includes a silicon base which defines a v-groove. An optical fiber can be positioned within the v-groove and a ball lens can be disposed adjacent an end portion of the optical fiber to form an optical fiber sub-assembly. The optical fiber sub-assembly can be mated with a second optical fiber sub-assembly, also comprised of an optical fiber and a ball lens mounted to a silicon base, such that the optical signals transmitted by a first optical fiber are collimated by the pair of ball lenses so as to be efficiently coupled to the second optical fiber. In order to prevent unnecessary exposure of the optical fiber to potentially harmful environmental influences, the optical fiber sub-assemblies can be disposed within respective self-sealing connector enclosures. In order to allow the first and second optical sub-assemblies to be mated, however, at least one of the connector assemblies has a spring-loaded cover that retracts upwardly to receive a corresponding portion of the other connector enclosure.
The fiber optic connector disclosed by R. J. Pimpinella as well as the above-described alignment methods and systems do not provide for the precise alignment of one or more optical fibers within a hermetically sealed package, such as a hermetically sealed fiber optic connector. Instead, the retraction of the spring-loaded cover of the connector enclosure of the fiber optic connector disclosed by R. J. Pimpinella can allow contaminants or moisture to enter the connector enclosure. In addition, the fiber optic connector disclosed by R. J. Pimpinella does not provide for realignment of the optical fibers without replacing the silicon bases in which respective v-grooves are defined. Further, the fiber optic connector disclosed by R. J. Pimpinella is also relatively difficult due to the recessed areas adjacent the ball lens.
As known to those skilled in the art, the precise alignment of an optical fiber within a hermetically sealed package is complicated since, in addition to precisely aligning the optical fiber in each of the six degrees of freedom, the alignment process must typically be performed without physically contacting or otherwise heating the optical fiber since heat, such as body heat, can cause the optical fiber to move due to thermal expansion, thereby misaligning the optical fiber. In addition, access to an optical fiber within a hermetically sealed package is generally limited since the optical device with which the optical fiber is being aligned is disposed within an internal cavity defined within the hermetic package.